By certain production/manufacturing methods there is a need of interior machining of a work piece, to more or less complicated internal geometries, for example by manufacturing of valves, engine blocks hydraulic details and the like. Then a need of temporary hole-makings often arises, for access to drill, mill or in another way machine, the interior in those spaces that has to be machined, to intended geometry. After the interior geometries are machined, the temporary made holes, in several cases, must be sealed. For applications exposed by low pressures, fluid pressures, or air pressures, there are a lot of solutions for the sealing of the holes. On the other hand for high pressures, especially in the range of 100 bar and above, there are few solutions that are able to give a satisfactory sealing. There are known constructions for these high ranges of pressure where the solutions foremost are of the type expanding plug of metal, provided of a cylindrical sleeve and some form of core inside the sleeve, or which can be introduced in the same. A frequent solution is a plug of the art pop rivet, with a cylindrical sleeve with a through shaft for engagement with a special tool, which by activating grips the shaft and moves the shaft in relation to the sleeve, whereby the wedge shaped part of the shaft enters the sleeve, and accordingly the sleeve expands outwards to the walls of the hole that surrounds the plug. The sleeve often comprises some form of ribs at its outside, and further the sleeve is usually of harder material as the material that has to be plugged. By the expansion the walls of the hole are deformed plastically whereby a sealing is obtained between the plug and the wall of the hole.
Other types of expanding plug that works in a similar way, consists of a sleeve, whose one end has a bottom and the other end an opening, and where the sleeve is provided with ribs at its outside. The bottom also works as a guide for the plug by the entry of the plug in the hole that has to be sealed. At the opening of the sleeve a ball is provided to be pressed into the sleeve. By means of a special hammer or a special stop the ball is knocked into the sleeve that than expands, whereby the sleeve engages in the walls of the hole by that those at the same time are plastically deformed and a satisfactory sealing is obtained.
A third type of expanding plug is constituted only of a cylindrical sleeve with a guiding bottom at its one end and an open side at its other end, and some sort of ribs provided at the outside of the sleeve. Instead of a ball as expanding driver a tool is used directly in the opening of the sleeve, where the plugging is performed by that the tool is knocked into the adapted opening in the sleeve, whereby the sleeve is urged to expand outwards to the walls of the hole and a sealing is obtained.
There is also a solution according to EP 0951626, which offers an improved sealing plug or a fastening element to a usual standard, a so called NPTF-thread. A NTPF-thread is types of thread developed in USA according to national standards, and are known in the range of pipe plug threads and NPTF stands for National Pipe Thread Standards-Fuel and Oil. The NPTF-thread is a conical designed thread that is used in a before thread-cut pipe or work piece, which pipe or work piece first is prepared with drilling of a hole with parallel walls, which thereafter are broached to achieve a conical hole. According to the patent the standard thread (NPTF) gives a first sealing by deformation of the tops of the inner and outer thread, but no satisfactory sealing is obtained against for instance creeping leakage of fluids based of capillary effects and additionally there is a risk of so called cross threading which can result in an untighten thread. To overcome those disadvantages a plug according to the patent is invented with partly a threaded part and a second sealing part with several different forms of embodiments. The second sealing part is provided at the front end of the plug, while the threaded part is provided at its back end. Between those parts there is a middle part. The thread is designed as a standard type of cutting thread, which must bring about the so called NPTF-thread and the hole that it has to seal must be broached to a conical shape before the plugging can be done. The second part, the sealing part on the other hand has no thread, the sealing is obtained by that the plug is driven in by the above mentioned thread to such depth that the second sealing part grips and bites in to or deform the smooth broached and conical wall of the hole. The sealing part is constituted of a ring or rings, or only a bulb or straight or conical end part which by driving in deforms the wall of the hole and causes a sealing by the material that “swells out” in front of the sealing part.